The present invention relates to a black pigment ink, particularly, to an ink suitable for ink jet recording which is carried out by squirting ink droplets from a printing head, and, more particularly, to a black pigment ink which can give printed images of excellent quality and high light resistance.
In the conventional ink jet recording, dye inks prepared by dissolving various dyes in water or mixed solvents of water and organic solvents have been used.
However, dye inks have the disadvantage that they are apt thereby blot on the recording paper to deteriorating the quality of the resulting printed images, and furthermore, the resulting images are inferior in light resistance and water resistance.
Under these circumstances, an investigation has been made to prepare pigment inks which have less blotting and can provide printed images which are excellent in quality and high in both light and water resistance. However, conventional pigment inks suffer from poor dispersibility and dispersion stability of the pigment particles in the ink and, furthermore, they are likely to cause clogging of the printing head. One of the methods for the solution of these problems is proposed in JP-A-3-210373. It discloses an aqueous pigment ink prepared using acidic carbon black. The reference teaches that acidic carbon black enhances affinity of the pigment particles per se for an aqueous solvent, resulting in improved image density.
However, the aqueous pigment ink disclosed in JP-A-3-210373 is soluble in an aqueous solution and is prepared by dissolving an amine in a dispersant and the dispersant, per se, has an acidic polar group such as carboxyl group. Since both the pigment and the dispersant have acidity, the dispersibility of the dispersant for pigment is not so high. As a result, clogging at the printing head is apt to occur and, further, the resultant printed images are insufficient in quality.